In recent years, when an independent channel called an eigenmode is used by an SVD (Singular Value Decomposition) scheme in the MIMO (Multiple Input Multiple Output) communication using a plurality of antennas in transmission and reception of data, a communication system has dramatically increased the transmission capacity by controlling transmission power and a modulation scheme of each eigenmode according to an eigenvalue of the eigenmode. However, transmission characteristics are seriously deteriorated in the MIMO communication using the eigenmodes, if orthogonality collapses for some reason.
In order to address such a problem, Patent Document 1 suggests, with a Doppler frequency or the likes as known information, to prevent the characteristic deterioration when the orthogonality collapses, by calculating SINR (Signal to Interference plus Noise Ratio) based on the known information and performing control. Patent Document 1 concerns that a slot to estimate a channel differs from a slot to actually transmit data and that the channel varies due to Doppler variation. As a technique to solve such problems, the document suggests a MIMO eigenmode adaptive transmission system to calculate a value of SINR of the eigenmode based on an estimated value of a channel estimation error due to Doppler variation, an estimated value of loss of gain of an eigenbeam and an estimated value of interference between eigenbeams, and thereby incorporating an adaptive coding modulation function and a simple and highly effective adaptive power control function in consideration of the actual environment having the Doppler variation.
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-252834